An explicit solvent model of coacervate structure and thermodynamics

Area of Science:

• Polymer Science
• Physical Chemistry
• Materials Science

Background:

• Complex coacervation is a liquid-liquid phase separation driven by electrostatic interactions between oppositely charged polyelectrolytes (PEs).
• It is relevant in biological systems and has potential applications in materials science.
• A molecular-level understanding of the internal structure of the complex coacervate phase is lacking.

Purpose of the Study:

• To investigate the effects of polyelectrolyte degree of polymerization (N) on phase behavior and internal structure.
• To gain molecular-level insights into complex coacervation using simulations.
• To explore the interplay of electrostatics and chemistry in solvated polyions.

Main Methods:

• Molecular dynamics simulations using a bead-spring model for polyelectrolytes.
• Inclusion of explicit nonpolar solvents.
• Analysis of phase behavior and internal structure as a function of polymer length (N).

Main Results:

• Coacervate phase stability increases with N, elevating the critical temperature.
• Polyelectrolytes in the dense phase exhibit a homogeneous, overlapping distribution, avoiding globule collapse.
• Dense phase compactness increases with N, consistent with experimental data, despite increased polymer size (radius of gyration).

Conclusions:

• The degree of polymerization significantly influences complex coacervation phase behavior and internal structure.
• Simulations provide a molecular-level understanding of coacervate phase formation.
• This work serves as a foundation for studying the combined roles of electrostatics and chemistry in polyion behavior.